The present invention relates to a new group of alkaline proteases that are especially stable in the presence of detergents and bleaches. More particularly, the present invention relates to proteases that can be obtained, for example, from a particular class of soil bacteria and that are generally useful in heavy-duty detergent liquids (HDLs) which contain linear alkylbenzene sulfonate.
Alkaline proteases are commonly added to HDLs because of the ability of these enzymes to decompose proteinaceous stains. These enzymes perform at the high pHs which are beneficial to the detergency of the surfactants in these formulations. Exemplary of such alkaline proteases, which are generally from Bacillus species, are Esperase.TM., Savinase.TM. and Alcalase.TM. from Novo Nordisk Bioindustrials Inc. and Maxatase.TM. and Maxacal.TM. from Gist-Brocades N.V. Although these enzymes have an optimal pH for activity of from 9 to 11, they rapidly lose their activity when stored at pH 10 to 11 in HDLs. This is especially true in HDLs with a high concentration of alkylbenzene sulfonates, such as linear alkylbenzene sulfonate (LAS). While anionic surfactants such as LAS provide excellent detergency at a low cost, they appear to be particularly detrimental to enzyme stability as compared to nonionic surfactants. See, for example, Kravetz et al., Am. Oil Chem. Soc. 62: 943 (1985).
Several patents relate to the stabilization of alkaline proteases in HDLs. Stabilization agents which have been used include formate and alcohols (U.S. Pat. No. 4,318,818), boric acid (U.S. Pat. No. 4,537,706), a combination of boron compounds, glycerin and a carboxylic acid (U.S. Pat. No. 4,900,475) and dicarboxylic acids and boric acid (GB patent application No. 21 26 242). But these stabilization systems do not sufficiently extend the lifetime of proteases, especially in high performance formulations having both a high pH and a high concentration of anionic surfactants.
Other patents relate to bacteria which produce alkaline proteases characterized by one or more properties. See, for example, U.S. Pat. Nos. 4,797,362, 4,771,003, 4,764,470, 3,838,009, 3,827,643 and 3,674,643. All of these patents relate to alkaline proteases obtained from specific bacterial strains, yet none discloses how any disclosed bacterial strain was isolated or how desirable strains other than those deposited might be reproducibly obtained to produce an alkaline protease with advantageous properties.